<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .container {
      display: flex;
    }
    .item {
      width: 50px;
      height: 50px;
      background-color: blue;
    }
    .left {
      border-radius: 50px 0 0 0;
    }
    .right {
      border-radius: 0 50px 0 0;
    }
  </style>
</head>
<body>
  <div class="container">
    <div class="item left"></div>
    <div class="item right"></div>
  </div>
</body>
</html>